STRUCTURE, MORPHOLOGY, AND PHYSIOLOGY. 13 



example) the third glume of some is empty and there- 

 fore a sterile glume, while in others it bears a $ flower 

 or merely a sterile branch with the palea, in which case it 

 becomes a flowering glume ; but this by no means makes 

 all Panicums two-flowered, any more than we would 

 call Leucojum vemum a three-flowered plant because 

 both of its enrpty bracts bear flowers in other species 

 of the same genus. In most and the best works (e.g., 

 Kunth's, but not Bentham's) this third glume is called a 

 neuter flower ("flos neuter"), a term whose meaning 

 should be always present to those desiring to use these 

 works. The empty glumes are often very like the 

 flowering, but are seldom awned. The flowering glumes 

 assume many forms and are frequently awned ; they 

 almost always have a middle nerve. At their point of 

 insertion they frequently extend downwards a little on 

 the axis of the spikelet ; this portion which is grown to 

 the axis is separated from the free portion by a more or 

 less distinct furrow and is called the callus ; it occurs 

 also upon many empty glumes (Heteropogon contortus R. 

 & Sch.), is frequently hairy, and in the fruiting glumes 

 serves to fasten them to other objects. (Compare Stipa, 

 Fig. 44, cal.) The palea, which with its enclosed flower 

 stands opposite to the flowering glume, does not belong to 

 the main axis of the spikelet, but to the branch which bears 

 the flower. That this relation of parts may be gradually 

 obliterated in the one-flowered grasses, and that the 

 palea may be moved back upon the main axis, has been 

 explained above. As long as an axis or a rudiment of 

 one, at least in its earliest stage, is visible beyond the 

 palea, this latter possesses (like the prophylla of the 

 culm-branches) two keels, or at least two lateral nerves, 

 without a midrib ; only when all trace of the axis is 

 absent does the palea become from one- to many-nerved 

 (with a midrib) or nerveless. It is almost always of a 

 more delicate texture than the flowering glume, its edges 

 are usually turned in, and it has a furrow instead of a 

 midrib. The prophyllum of the culm-branches has no 

 blade, and the palea resembles it in being almost al- 

 ways (excepting Amphipogon) awnless ; and as the former 



